In semiconductor devices such as a 3D-NAND nonvolatile semiconductor storage device, a stairway structure may be provided in which a plurality of conductive films and insulating films are stacked one above another. In case a metal film is employed as the conductive films, it is required to form an etch stop film above the metal film when forming holes connecting to the terraces of the stairway structure. However, it has been a challenge to conceive device structures and processes enabling such arrangement.